Mat Table is not displaying data on ngOnIt but after refresh its displaying

问题

I'm using Angular Material with Angular.

My table does not display data on the ngOnInit lifecycle hook, but after I refresh the app it displays:

Even ChangeDetectorRef doesn't affect the table.

Here is the template for the table:

<div class="example-container mat-elevation-z8">
<mat-table #table [dataSource]="dataSource"> 
    <ng-container matColumnDef="Phone">
        <mat-header-cell *matHeaderCellDef> Phone </mat-header-cell>
        <mat-cell *matCellDef="let user"> {{ user.phone }} </mat-cell>
    </ng-container>
    <ng-container matColumnDef="LastName">
        <mat-header-cell *matHeaderCellDef> LastName </mat-header-cell>
        <mat-cell   *matCellDef="let user" > {{ user.lastname}} </mat-cell>
    </ng-container>

    <mat-header-row *matHeaderRowDef="displayedColumns"></mat-header-row>
        <mat-row *matRowDef="let user; columns: displayedColumns;"></mat-row>
    </mat-table>
    <mat-paginator [pageSizeOptions]="[5, 10, 25, 100]"></mat-paginator>
</div>

And here's the component's file:

import { ChangeDetectorRef } from '@angular/core';
import { MatTableDataSource } from '@angular/material';
import { UserService } from './user.service';

export class UsersComponent implements OnInit {
    constructor(private ref: ChangeDetectorRef, private userService: UserService){}
    displayedColumns = ['ID', 'FirstName', 'Phone', 'LastName'];
    dataSource: MatTableDataSource<User>;
    users: User[] = [];
    ngOnInit() {
        this.users= this.userService.getUserList();
        this.dataSource = new MatTableDataSource(this.users);
        this.ref.detectChanges();
    }

Here is a snippet of UserService for getting a user list:

getUserList() {
    const headers = new Headers({'Content-Type': 'application/json', 'Authorization': 'Bearer ' + this.authenticationService.token});
    const options = new RequestOptions({ headers: headers });
    this.http.get('/api/getallusers/', options)
     .map((data: Response) => {
         return data.json() as User[];
      }).toPromise().then(x => {
         this.userList = x;
      });
      return this.userList;
    }

回答1:

This issue was there with the beta version though and that could be resolved using detect changes.

In your case , the real issue is data is not getting assigned in ngOnit, you need to use Observables instead of Promise and subscribe inside the component, Change your service as follows,

 getPatients() {
    const headers = new Headers({ 'Content-Type': 'application/json', 'Authorization': 'Bearer ' + this.authenticationService.token });
    const options = new RequestOptions({ headers: headers });
    return this.http.get('/api/getallpatients/', options)
      .map((response: Response) => response.json());
  }

and call it inside the component as,

 ngOnInit() {
    this.patientService.getPatients().subscribe((data) => {
      this.patients = data;
      console.log('#####patients inside ngonit', this.patients);
      this.dataSource = new MatTableDataSource(this.patients);
    });

回答2:

Here is the answer:

ngAfterViewInit() {
  Your code here.
  }

来源：https://stackoverflow.com/questions/48186828/mat-table-is-not-displaying-data-on-ngonit-but-after-refresh-its-displaying